1. Field of Invention
The invention relates to a power module, and more particularly to a power module applied to a power converter.
2. Related Art
High efficiency and high power density are always the requirements on the power converter. The high efficiency represents that the energy consumption is decreased, and is advantageous to the energy saving, heat reduction, and environment protection, and the spent cost can be reduced. The high power density represents the small size and the light weight, and can decrease the transportation cost and the required space so that the building cost can be reduced. The high power density also represents the reduction of the used materials, and is further advantageous to the energy saving, heat reduction, and environment protection. Therefore, the seeking on the high efficiency and the power density in the power field becomes unceasing.
There are more kinds of power converters due to different applications of the power converters. The power converters may be classified into a non-isolated AC/DC power converter, a non-isolated DC/DC power converter, an isolated DC/DC converter, an isolated AC/DC power converter and DC/AC, AC/AC power converters according to the type of the electric energy being converted. The non-isolated AC/DC power converter is, for example, composed of an AC/DC conversion circuit for a power factor correction (hereinafter referred to as PFC) circuit. The isolated AC/DC power converter is composed of one PFC circuit and one or multiple DC/DC converters. Because the electric energy properties to be converted and the conversion levels are different, the power densities and efficiencies, which can be easily achieved by various converters, are not always the same. Taking the isolated AC/DC power converter as an example, the general industrial power density is 10 W/inch3, and the efficiency is about 90%. The non-isolated AC/DC power converter, the isolated DC/DC converter and the DC/AC power converter have the higher efficiencies and power densities.
As mentioned above, the high efficiency of the power converter represents the low energy consumption. If the efficiency is 90%, the converted energy consumption is equal to about 10% of the total input energy of the power converter. If the power converter has the efficiency of 91%, its converted energy consumption is reduced to 9% of the total input energy. That is, when the efficiency is increased by one point, the energy consumption is reduced by 10% as compared with the power converter with the efficiency of 90%, and the improvement is very considerable. In fact, the efforts on the efficiency improvement of the power converter are often proceeded with the order of magnitude equal to 0.5% or even 0.1%.
The energy consumption of the power converter is mainly composed of the on-state loss and the switch loss, especially the switch loss of the active device. The switch loss is more significantly affected by the working frequency. The power converter, especially the switch power converter, has the working frequency usually higher than 20 kHz in order to decrease the audio noise. The selection of the actual working frequency of the power converter is more significantly affected by the inactive device, especially the magnetic element. If the magnetic element has the small size, the high frequency is usually needed to decrease the magnetic flux density of the working element in order to achieve the reliable work. Thus, the high switch loss is induced. Alternatively, the wire diameter of the wire set and the number of loops in the magnetic element can be increased so that the on-state loss is increased and the high loss is further induced. On the contrary, if the magnetic element has the large size, the working frequency can be lowered under the precondition of assuring the reliable work, and the switch loss is thus decreased. Also, the wire diameter of the wire set and the number of loops in the magnetic element may be decreased, so that the on-state loss is decreased, the total loss is decreased and the high efficiency is obtained.
Therefore, it is easy to understand that one of the key factors of obtaining the high power density or the high efficiency is to enhance the space availability inside the power converter. As the space availability gets higher, the larger space for the inactive device, especially the magnetic element, which is very important to the power converting efficiency, is left. Thus, the large-size inactive element can be easily used so that the power efficiency is increased. Also, the total power of the power source can be increased by using the large-size inactive device, so that the power density of the power converter can be enhanced. Thus, for the high power space availability, the high efficiency can be achieved more easily under the specific power density, or the high power density can be achieved more easily under the specific efficiency, and it is possible to possess both the high power density and the high efficiency concurrently.
The semiconductor chip is one of the important factors of determining the efficiency of the power converter. However, the semiconductor chip usually unavoidably needs to use additional materials, such as the package material for protecting the semiconductor, the heat sink for dissipating heat, the fixture for fixing the semiconductor chip, and the like, which are useless to the electricity converting efficiency. The internal spatial availability of the power source becomes worse as the ratio of these materials to the power converter gets larger. Thus, the power semiconductor chip and the spatial volume occupied by the power chip are getting more and more emphasized.
In the integrated power module (IPM), many semiconductor chips are integrated in one chip package so that the spatial availability in the package may be enhanced. However, the space occupied by the power chip in the existing power module cannot be effectively decreased, and the existing power module is seldom used in the high-performance power converter.
In order to enhance the power density or converting efficiency of the power converter, a reasonable solution to the power module with the high space availability and the reasonable cost is required. The existing arts, however, cannot easily satisfy these conditions.